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The COVID-19 Infection Survey (CIS) aims to estimate:

  • how many people have the infection over a given time
  • how many new cases occur over a given period
  • how many people have antibodies to COVID-19.

The survey will help track the extent of infection and transmission of COVID-19 among people in private residences, referred to as the community population.

Proportion of people in Wales who had COVID-19

For the week of 17 to 23 October 2020 it is estimated that an average of 0.86% of the community population had COVID-19 (95% credible interval: 0.41% to 1.58%).

This equates to around 1 in 120 individuals (95% credible interval: 1 in 240 to 1 in 60), or an estimated 26,100 people in total (credible interval: 12,600 to 47,900).

The rate has increased in recent weeks. Since the estimates are based on a relatively low number of positive tests, there is a significant degree of uncertainty and the results should be interpreted with caution.

Chart showing the official estimates for the percentage of people testing positive through nose and throat swabs from 12 September to 23 October 2020. The trend has increased in recent weeks.



In September, 4.2% (95% confidence interval: 2.1% to 7.5%) of people aged 16 and over tested positive for antibodies to the coronavirus (COVID-19). The estimate is weighted to be representative of the overall population, and equates to around 1 in 24 people (95% confidence interval: 1 in 48, to 1 in 13), or around 107,000 individuals in total (95% confidence interval: 53,000 to 189,000).

Over the full course of survey from to July to 19October, an estimated 3.75% (95% confidence interval: 2.1% to 6.1%) tested positive for COVID-19 antibodies. Chart 2 gives monthly estimates from July, but since confidence intervals are wide, there is currently no evidence of a trend over time. Antibody levels in the blood can decline over time, meaning that some people who have previously had COVID-19 may subsequently test negative. For this reason, these figures should be regarded as estimates of monthly antibodies prevalence, not cumulative exposure.

Chart showing the official estimates for the percentage of people testing positive for COVID-19 antibodes through blood samples from July 2020. The confidence intervals are wide, meaning there is no evidence of a trend over time. In September, 4.2% tested positive.


One way the body fights infections like COVID-19 is by producing small particles in the blood called antibodies. It takes between two and three weeks for the body to make enough antibodies to fight the infection.

We measure the presence of antibodies to understand who has had COVID-19 in the past, although the length of time antibodies remain at detectable levels in the blood is not fully known. It is also not yet known how having detectable antibodies, now or at some time in the past, affects the chance of getting COVID-19 again.

Quality and methodology information

The results are based on nose and throat swabs provided by participants to the study. As well as looking at incidence overall, the survey will be used to examine the characteristics of those testing positive for COVID-19 and the extent to which those infected experience symptoms.

Fieldwork started in Wales on 29 June 2020. It is important to note that there is a significant degree of uncertainty with the estimates. This is because, despite a large sample of participants, the number of positive cases identified is small. Estimates are provided with 95% credible intervals to indicate the range within which we may be confident the true figure lies.

The results are for private households only and do not apply to those in hospitals, care homes or other institutional settings.

The Office for National Statistics (ONS) publishes weekly statistical bulletins and references tables, including results for England and Wales, on its website.

The estimates are based on statistical modelling. Modelling is carried out afresh each week using the latest 6 weeks’ data. The model works by smoothing the series to understand the trend and is revised each week to incorporate new test results. This means that the latest estimate for an earlier period may be different to the official estimate that was produced at the time. Chart 1 shows the latest modelled trend and the official estimates that were published at the time.

Samples from this survey are not yet large enough to support more detailed analysis than is provided here. Fieldwork is being scaled up with the intention of delivering approximately 9 thousand participants per fortnight by mid-December. This will enable more detailed analysis, which may include incidence (the number of new infections over a period of time) and analysis of the characteristics of people testing positive. The type of analysis that is possible will also depend on the underlying prevalence of the virus, with higher infection rates enabling more analysis and vice versa.

Further information about quality and methodology can be found on the ONS website.

Well-being of Future Generations Act (WFG)

The Well-being of Future Generations Act 2015 is about improving the social, economic, environmental and cultural well-being of Wales. The Act puts in place seven well-being goals for Wales. These are for a more equal, prosperous, resilient, healthier and globally responsible Wales, with cohesive communities and a vibrant culture and thriving Welsh language. Under section (10)(1) of the Act, the Welsh Ministers must (a) publish indicators (“national indicators”) that must be applied for the purpose of measuring progress towards the achievement of the Well-being goals, and (b) lay a copy of the national indicators before the National Assembly. The 46 national indicators were laid in March 2016.

Information on the indicators, along with narratives for each of the well-being goals and associated technical information is available in the Well-being of Wales report.

Further information on the Well-being of Future Generations (Wales) Act 2015.

The statistics included in this release could also provide supporting narrative to the national indicators and be used by public services boards in relation to their local well-being assessments and local well-being plans.

Contact details

Statistician: Ryan Pike
Telephone: 0300 025 6415

Media: 0300 025 8099

SFR 184/2020